My latest topic of interest is the series of collapsing practice string instruments invented by Ernest Nussbaum.  He started with a collapsing violin and viola and made two piece bows as well.  He quickly migrated to the collapsing electrified cello (patent D272,747 of Feb 21, 1984) and collapsing practice cello (patent D301,251 of May 23, 1989).  The collapsing practice cello enjoyed some commercial success and continues to be made by Jerry de Groot (Mr. Nussbaum died a few years ago).

Plans were once sold (back pages of Popular Mechanics style) some years ago but are no longer available (I would love to obtain a set to copy of anyone should have one).  Spruce wood comprised the structural members.  Later examples utilize Peghead planetary pegs.  

I sent an email to Mr. de Groot with a number of questions and he quickly responded.  I wondered if a collapsing string bass was possible.  Mr. de Groot said yes.  He has the materials but needs time.